The application of electronics in automobile mechanical systems for better performance is increasing the percentage of electronics parts in an automobile system day by day. Demand for accurate, reliable and non-contact sensors which are essential parts of electronic control is also increasing. For example, rotary position sensors are sensors used for sensing the rotational position of the shafts, axles or columns such as steering columns. The output from rotary position sensors comprises rotation position. Rotation position refers to the orientation of the shaft and the number of turns the shaft is rotated from the beginning of the reference position.
Rotary position sensors are used as steering wheel sensors. A steering wheel sensor provides the value of the angular position of a steering column of a vehicle. Use of this measured angle can be used, for example, in electrical power steering (EPS), active steering, advanced front lighting systems, lane departure warning systems, 4-wheel steering, and active suspension. EPS improves safety, generally make steering hydraulics obsolete, can cut fuel consumption by as much as 0.41/100 km, and reduce development time and assembly cost.
There are different available apparatus and related methods for measuring the steering wheel angle including a potentiometer, optical encoder, Hall-effect and anisotropic magnetoresistive (AMR) sensor. The potentiometer is simplest method and is very low cost solution for the measurement of steering wheel angle. However, potentiometers generally have very short lives because of sliding contacts which tend to wear out after prolonged use. Optical encoding is a contactless method used in steering wheel angle measurement but requires a counter or register for measurement of angle because it can measure only 360° at a time and the next rotation it is added to the last value using the counter or rotation register. Optical encoding has several disadvantages including reliability problems due to dust or mud which can easily damage the optical sensor.
Hall-effect and related AMR sensing represents another method. A large number of sensors elements are required, together with the necessity for the magnet to be aligned with Hall IC. These methods generally require a step-down gear mechanism for angle requirements more than 360° which will affect the resolution of sensor also introduce accuracy error and hysteresis due to backlash and wear and tear.
In view of the shortcomings of known rotary position sensors described above, there is a need for a sensor that reliably provides a linear output over a sensing range more than 360 degrees. Such a sensor would include a memory which is independent of power, and be self-error compensating for wear and tear which can happen over time during service life of the sensor.